The fuel cell is known to have the stack structure obtained by alternately stacking a plurality of membrane electrode assemblies (hereinafter referred to as “MEA”), wherein each MEA includes electrode layers formed on respective surfaces of an electrolyte membrane, and separators that separate adjacent membrane electrode assemblies. Each of the separators in the fuel cell has a flow channel configured to make a flow of hydrogen gas toward an anode side of the MEA, a flow channel configured to make a flow of an oxidizing gas toward a cathode side of the MEA and a flow channel configured to make a flow of a coolant for cooling down the fuel cell. During power generation by the fuel cell, water is produced on the cathode side of the MEA accompanied with the electrochemical reaction of hydrogen with oxygen. This produced water in the MEA may be frozen in a cold environment. This may lead to significant degradation of the MEA.
During a start-up of the fuel cell in the cold environment, one proposed technique suspends the feed of cooling water to the fuel cell until a rise of the temperature of the fuel cell, so as to prevent an extreme temperature decrease of the fuel cell by the flow of cooling water (for example, Patent Literature 1).